1. Field of the Invention
The present invention relates to a plasma addressed liquid crystal display device having a flat panel structure where a liquid crystal cell is superposed on a plasma cell, and more particularly to the shape of an intermediate substrate (microsheet) disposed between a liquid crystal cell and a plasma cell for separating them from each other. Further the invention relates also to a processing technique adopted in assembling a liquid crystal cell on a plasma cell.
2. Description of the Related Art
There is known a plasma addressed display device where a plasma cell is utilized for addressing a liquid crystal cell, as disclosed for example in Japanese Patent Laid-open No. Hei 4-265931 which corresponds to U.S. patent application Ser. No. 07/837,961 for an Electro Optical Device, filed by Shigeki Miyazaki on Feb. 20, 1992. As shown in FIG. 4, the above plasma addressed display device has a flat panel structure comprising a liquid crystal cell 101, a plasma cell 102 and a common intermediate substrate 103 interposed therebetween. The intermediate substrate 103 is composed of an extremely thin glass sheet or the like and is termed a microsheet. The plasma cell 102 consists of a rear substrate 104 joined to the intermediate substrate 103, and an ionizable gas is contained hermetically in a space defined therebetween. Striped discharge electrodes 105 are formed on an inner surface of the rear substrate 104. Since the discharge electrodes 105 can be produced through print baking on the flat rear substrate 104 by a screen printing process or the like, it is possible to attain superior productivity and workability with another advantage of adequacy for miniaturization. Barrier ribs 106 are formed on the discharge electrodes 105 to divide the space where the ionizable gas is hermetically contained, thereby constituting discharge channels 107. The barrier ribs 106 can also be baked by a screen printing process, and the respective tops thereof abut on one surface of the intermediate substrate 103. The striped discharge electrodes 105 function as anodes A and cathodes K alternately to generate plasma discharge therebetween. The intermediate substrate 103 and the rear substrate 104 are joined to each other by the use of glass frit 108 or the like.
Meanwhile the liquid crystal cell 101 is composed of a transparent front substrate 109. The front substrate 109 is bonded to the other surface of the intermediate substrate 103 with a predetermined gap retained therebetween by the use of a sealant 110 or the like, and the gap is filled with a liquid crystal 111. Data electrodes 112 are formed on the inner surface of the front substrate 109 in a manner to be orthogonal to the striped discharge electrodes 105. And matrix pixels are prescribed at the intersections of the data electrodes 112 and the discharge channels 107.
In the plasma addressed display device of the structure mentioned above, display driving is performed by line-sequentially switching and scanning the row discharge channels 107 where plasma discharges are generated and simultaneously applying, in synchronism with the scanning, picture signals to the column data electrodes 112 on the side of the liquid crystal cell 101. Upon generation of plasma discharges in the discharge channels 107, the inside is turned to the anode potential substantially uniformly, and the pixels are selected per row. That is, each discharge channel functions as a sampling switch. When a picture signal is applied to each pixel in a conducting state of the plasma sampling switch, the sampled pixel can be turn on or off under control. And even after the plasma sampling switch is turned to its non-conducting state, the picture signal is still held in the related pixel.
The intermediate substrate 103, which physically separates the liquid crystal cell 101 and the plasma cell 102 from each other, has an extremely small thickness of 50 .mu.m or so for electrically coupling the two cells. Therefore the intermediate substrate 103 is termed a microsheet. The front substrate 109 is bonded onto such microsheet through the sealant 110 with a gap retained therebetween, and the gap is filled with the liquid crystal 111 hermetically to constitute the liquid crystal cell 101. This gap has a further smaller dimension of 5 .mu.m or so. And for the purpose of ensuring a stable superior picture quality on the display, it is requisite to achieve uniform dimensional control of the gap over the entire display area. However, it has been difficult heretofore to realize satisfactory uniform control of the gap dimension.